The invention generally relates to a skew correction circuit.
Computer devices typically use buses to communicate with each other. In this manner, the bus typically include data lines that propagate data signals for purposes of communicating data between the devices. For purposes of synchronizing the capture of the data by the receiving device, or receiver, the transmitting device, or transmitter, may furnish a strobe signal (to a strobe line of the bus) that accompanies the data signals in a technique called source synchronous signaling.
In this manner, in source synchronous signaling, the strobe signal and data signals are synchronized together at the transmitter, the source of the transmitted signals. The strobe signal includes edges to which the receiver responds to latch the data signals at the appropriate times. Because the strobe signal propagates approximately along the same signal path as the data signals, the strobe signal experiences approximately the same delay as the data signals. However, the signal paths are not identical, and thus, a delay, or skew, may exist at the receiver between each data signal and the strobe signal. Therefore, typically the receiver includes circuitry, such as fixed delay lines, to adjust the timing of the strobe and/or data signals to accommodate any relative delay, or skew, between the strobe signal and the data signals.
There are two approaches that are commonly used to implement source synchronous signaling: quadrature strobing and coincident strobing. Quadrature strobing centers each data eye, or cell, of a data signal 10 (see FIG. 1) with edges of a data strobe signal 12 (see FIG. 2). For example, a particular data cell 14 of the data signal 10 may be aligned with a particular edge 15 of the data strobe signal 12 at time T1. With quadrature strobing, the misalignment of the strobe signal with the data signal is a function of the skew that is introduced by the transmitter, the interconnect bus lines and the receiver. Therefore, this skew may cause the edges of the data strobe signal to fall well outside of the center of the data eyes of the data signal.
With coincident strobing, the transmitter aligns the edges of the data signal and a strobe signal so that the signals are driven simultaneously onto the bus. For example, a particular edge 17 (see FIG. 3) of a data strobe signal 16 may be used to cause the receiver to capture a bit of data that is indicated by an eye 18 of the data signal 10. Due to the coincident strobing, at the transmitter, the eye 18 begins appearing on the bus at the same time (time T2) at which the edge 17 appears. The receiver typically delays the data strobe signal 16 via a fixed delay line to center the edge 17 in the eye 18.
Because a different skew may exist between each data signal and the strobe signal, the above-described techniques may not eliminate all of the skews between the data signals and the strobe signal. Furthermore, the skew may not be fixed, but rather, the skew may vary over time due to temperature and/or voltage variations.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above.